Abstract
The plate specimen of 18-8 austenitic steel was fatigued by the cyclic bending fatigue testing machine, and the dislocation structures beneath the specimen surface and around the fatigue microcrack were examined through the transmission electron microscope operated at 100 kV. Based on the experimental results the fatigue crack initiation was discussed. The main results obtained are as follows:
(1) The dislocation arrangement beneath the surface of the specimen fatigued at a low stress amplitude is closely related to the surface deformation markings. Namely, the dislocations array in the same form as that in single or multiple slip lines. On the other hand, the cell structure formed at a high stress amplitude has no correlation with surface markings.
(2) The densely concentrated dislocations and stacking faults align along the {111} trace in the localized region just beneath the surface, and this structure represents the underlying structure of the persistent slip band. On the other hand, the ladder structure might be formed in such a region of about 20 μ beneath the surface. The fatigue crack initiates in this area.
(3) The well-defined cell structure is formed in the vicinity of fatigue microcrack, and the fatigue crack runs along the {111} trace independently of the cell wall.
